Polymeric prosthetic liners (hereinafter also referred to as “prosthetic liners” or “liners”) have become the interface of choice among amputees due to various beneficial characteristics thereof. These characteristics include, for example, comfort, security of suspension, protection of the residual limb, and ease of use. Modern liner technology allows amputees to employ a liner as the sole (stand-alone) interface between their residual limb (which is also commonly referred to as a residuum or amputation stump) and the interior of a prosthetic socket.
Polymeric prosthetic liners generally come in two primary forms—with a distal connecting element or without a distal connecting element. Prosthetic liners that lack a connecting element are commonly referred to as “cushion liners,” although such liners can still serve a suspensory function. Prosthetic liners that include a connecting element, which acts to facilitate suspension by mechanical attachment of the liner to a prosthesis, are commonly referred to as “locking liners.” Prosthetic liners can be of standard “off-the-shelf” design, meaning the liner is of generic shape and will fit a range of residual limb shapes and sizes. Alternatively, liners may be custom designed for a particular amputee.
Liners may be comprised of various polymeric materials; including silicone, urethane, and thermoplastic elastomer (TPE) gels. Liners are now commonly made using various block copolymer and mineral oil gel compositions, as well as silicone and blended silicone compositions. Such polymeric materials have proven themselves to provide a high level of comfort for most users.
It is also known to construct such liners with an outer layer of fabric. That is, there exist patented fabric-covered liners having an interior of exposed polymeric gel for contacting and cushioning an amputee's residual limb, and an outer layer of fabric for, among other things, increasing the wear resistance of the liner, and facilitating donning/doffing and insertion of the liner-covered residual limb into a prosthetic socket. Such patented fabric-covered liner products are available from The Ohio Willow Wood Company in Mt. Sterling, Ohio.
Liners as described above may be used by upper limb amputees but are probably more frequently used by lower limb amputees. Lower limb amputees generally fall into one of two categories: below knee (BK) amputees and above knee (AK) amputees. In the case of a BK amputee, the amputation may occur through the tibia (i.e., is trans-tibial) or through the ankle (i.e., a Syme's amputation) and the knee joint is still present on the residual limb. Thus, a bending of the residual limb at the knee joint will still occur during ambulation. In the case of an AK amputee, the amputation may occur through the femur (i.e., is trans-femoral) or knee (i.e., a knee disarticulation) and the knee joint is missing from the residual limb.
In any case, and as would be well understood by one of skill in the art, an amputee typically dons a prosthetic liner, such as by rolling it onto the residual limb, and then inserts the liner-covered residual limb into a socket portion of a prosthesis. The prosthesis may be suspended (secured) on the liner-covered limb by means of, for example, vacuum, by a mechanical attachment such as a pin and lock mechanism, by friction alone, by use of a suspension sleeve, or by a combination thereof.
As would also be understood by one of skill in the art, a residual limb can become quite warm when covered with a polymeric prosthetic such as those described above, due largely to the substantially non-breathable and minimally thermally conductive nature of the silicone, urethane, TPE and other polymeric materials that are generally used. This heat retention problem may be further compounded when the exterior of the polymeric material is covered with a fabric, as described above. As it is desirable to employ a fabric that is durable and will prevent the bleed-through of polymeric material to the exterior of the fabric, the fabric may itself serve as another cause of heat retention.
The prosthetic socket into which a liner-covered residual limb is inserted may also contribute to the aforementioned heat retention problem. Since prosthetic sockets are commonly formed from fiberglass, composites, thermoplastics, resins, and other rigid and impermeable or substantially impermeable materials with comparably low thermal conductivities, heat transfer through the prosthetic socket is typically inhibited if not prevented.
As can be understood then, when a polymeric liner-covered residual limb is inserted into a prosthetic socket, both the liner and the prosthetic socket may cause the residual limb to retain heat. This effect may be exacerbated when the prosthetic liner also includes a fabric-covered exterior. If a suspension sleeve is used, it too can contribute to the heat retention problem, since such sleeves are also typically of a polymer and fabric construction. The results of this heat retention may include, for example, an uncomfortable warming of the residual limb and/or excessive perspiration that can lead to skin problems. In fact, at least one study has shown that heat/sweating in the prosthetic socket is considered by many amputees to be the predominant problem associated with the wearing of a prosthesis. (See e.g., Consequences of non-vascular trans-femoral amputation: a survey of quality of life, prosthetic use and problems, K. Hagberg and R. Branemark, Prosthetics and Orthotics International, 2001, 25, 186-194).
In recognition of this residual limb heating problem, commercially available prosthetic liners and sockets have been analyzed with respect to their thermal conductivity properties and it has been shown that both prosthetic liners and prosthetic sockets contribute to residual limb heating. One such study reveals that a sample of several commercially available prosthetic liners exhibits a thermal conductivity of between 0.085-0.266 W/(m·° K), while a sample of several commercially available prosthetic socket materials exhibits a thermal conductivity of between 0.148-0.150 W/(m·° K). (See The thermal conductivity of prosthetic sockets and liners, G. K. Klute, G. I. Rowe, A. V. Mamishev, & W. R. Ledoux, Prosthetics and Orthotics International, September 2007, 31(3), 292-299.)
Similarly, orthotic devices can also suffer from heat retention problems. For example, knee sleeves and braces, ankle-foot orthoses (AFOs), knee-ankle-foot orthoses (KAFOs), walker boots, shoe insoles, back braces, and other braces can include polymers for padding, fabrics, resins, and reinforcements as used in prosthetic liners and sockets.
Importantly, patient testing has revealed that humans are capable of detecting the results of even small improvements in thermal conductivity when it comes to a device such as a prosthetic liner. For example, test patients unsolicitedly reported a perceived reduction in residual limb temperature (i.e., their residual limbs felt cooler) when wearing prosthetic liners whose polymeric material was silicone instead of a block copolymer and mineral oil gel composition. This is despite the fact that the difference in thermal conductivity between the particular silicone material and block copolymer and mineral oil gel composition in question was only about 0.04 W/(m·° K). Consequently, enhancing the thermal conductivity of prosthetic and/or orthotic devices to an even more substantial degree may bring about even greater patient comfort through further reduced limb temperatures.
It can be understood from the foregoing discussion that there is a need for various prosthetic and orthotic devices that maximize heat transfer from the associated residual limb or intact limb of the user and/or provide for the enhanced absorption of residual limb heat—the meaning of which is explained in more detail below. Exemplary prosthetic devices and assemblies according to the invention may include, without limitation, a polymeric prosthetic liner, a prosthetic suspension sleeve, a prosthetic socket, and a prosthetic assembly that includes such a prosthetic liner along with a prosthetic socket and, optionally, a prosthetic suspension sleeve. Such orthotic devices may include, without limitation, an AFO, a KAFO, a knee sleeve, a walker boot, a shoe insole, a back brace, and other braces, as mentioned above, as well as any other orthotic device that includes similar materials of construction.